Gas generant compositions

ABSTRACT

A gas generant composition is provided that contains a transitional metal salt of 5-aminotetrazole and phase stabilized ammonium nitrate. A gas generator incorporating the gas generant composition is also provided. The gas generator may be contained within a gas generating system such as an airbag inflator or seat belt assembly, or more broadly within a vehicle occupant protection system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 60/810,006 filed on May 31, 2006.

TECHNICAL FIELD

The present invention relates generally to gas generating systems, and to gas generating compositions employed in gas generator devices for automotive restraint systems, for example.

BACKGROUND OF THE INVENTION

The present invention relates to gas generant compositions that upon combustion produce a relatively smaller amount of solids and a relatively abundant amount of gas. It is an ongoing challenge to reduce the amount of solids and increase the amount of gas thereby decreasing the filtration requirements for an inflator. As a result, the filter may be either reduced in size or eliminated altogether thereby reducing the weight and/or size of the inflator. Additionally, reduction of combustion solids provides relatively greater amounts of gaseous products per gram or unit of gas generating composition. Accordingly, less gas generant is required when greater mols of gas are produced per gram of gas generant. The result is typically a smaller and less expensive inflator due to reduced manufacturing complexity.

Yet another concern is that the compositions must exhibit burn rates that are satisfactory with regard to use in vehicle occupant protection systems. In particular, compositions containing phase stabilized ammonium nitrate may exhibit relatively lower burn rates requiring various measures to improve the burn rate. Accordingly, the development of energetic fuels is one ongoing research emphasis whereby the less aggressive burn characteristics of preferred oxidizers such as phase stabilized ammonium nitrate are accommodated and compensated.

SUMMARY OF THE INVENTION

The above-referenced concerns are resolved by novel gas generant compositions. A fuel constituent or compound is selected from transitional metal salts of 5-aminotetrazole including copper 5-aminotetrazole, nickel 5-aminotetrazole, zinc 5-aminotetrazole. Phase stabilized ammonium nitrate, stabilized in a known manner, is included as a primary oxidizer.

An optional second fuel may be selected from tetrazoles and salts thereof, triazoles and salts thereof, azoles and salts thereof, guanidines and salts thereof, guanidine derivatives, amides, and mixtures thereof. An optional secondary oxidizer is selected from metal and nonmetal nitrates, nitrites, chlorates, perchlorates, oxides, other known oxidizers, and mixtures thereof.

In further accordance with the present invention, a gas generator or gas generating system, and a vehicle occupant protection system incorporating the gas generant composition are also included.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view showing the general structure of an inflator in accordance with the present invention.

FIG. 2 is a schematic representation of an exemplary vehicle occupant restraint system containing a gas generant composition in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a gas generant system that includes at least one of the following: improved ability to prevent formation of a low-melting point eutectic, improved effluent quality, enhanced thermal stability, and/or improved burn rates when employing phase-stabilized ammonium nitrate as an oxidizer. Accordingly, gas generant compositions containing a transitional metal salt of 5-aminotetrazole and phase-stabilized ammonium nitrate (PSAN) are provided. The PSAN may for example, contain about 10% potassium nitrate coprecipitated within ammonium nitrate in a known manner. This combination results in gas generant compositions that exhibit a burn rate of 0.8 ips at 1500 psi or 1.5 ips at 5500 psi, and/or, provide thermal stability at 107 C for over 400 hours.

In one embodiment, the copper salt of 5-aminotetrazole is provided as a fuel at about 70% by weight of the total gas generant composition. Phase-stabilized ammonium nitrate is provided at about 30% by weight of the total gas generant composition. In general, a fuel component containing a transitional metal salt of 5-aminotetrazole, including nickel, magnesium, zinc, or copper complexes/salts of 5-AT, may be provided at about 5-70 wt. % of the composition. An oxidizing component, including phase-stabilized ammonium nitrate, may be provided at about 5-70 wt. %.

Secondary fuels include tetrazoles such as 5-aminotetrazole; metal salts of azoles such as potassium 5-aminotetrazole; nonmetal salts of azoles such as diammonium salt of 5,5′-bis-1H-tetrazole: nitrate salts of azoles such as 5-aminotetrazole; nitramine derivatives of azoles such as 5-aminotetrazole; metal salts of nitramine derivatives of azoles such as dipotassium 5-aminotetrazole; metal salts of nitramine derivatives of azoles such as dipotassium 5-aminotetrazole; nonmetal salts of nitramine derivatives of azoles such as monoammonium 5-aminotetrazole and; guanidines such as dicyandiamide; salts of guanidines such as guanidine nitrate; nitro derivatives of guanidines such as nitroguanidine; azoamides such as azodicarbonamide; nitrate salts of azoamides such as azodicarbonamidine dinitrate; and mixtures thereof. If desired, these fuels are provided at about 0.1-25 wt. percent of the total composition. When combined with the transitional metal complex of 5-aminotetrazole, are provided at about 5-70 wt. percent of the total composition. A preferred amount of fuel is about 30 wt. percent of the total composition.

Secondary oxidizers include metal nitrates such as strontium nitrate and potassium nitrate; metal nitrite salts such as potassium nitrite; metal oxides such as iron oxide; non-metal or metal perchlorates or chlorates such as ammonium perchlorate and potassium perchlorate; and other oxidizers recognized by those of ordinary skill. If desired, these oxidizers are provided at about 0.1-25 wt. percent of the total composition.

Processing aids such as fumed silica, boron nitride, and graphite may also be employed. Accordingly, the gas generant may be safely compressed into tablets, or slugged and then granulated. The gas generant may also include binders such as cellulose derivatives, cellulose acetate, and cellulose acetate butyrate, and carboxymethylcellulose, salts of carboxymethylcellulose; silicone; polyalkene carbonates such as polypropylene carbonate and polyethylene carbonate. The processing aid and/or binder is generally provided at about 0-15 wt %, and more preferably at about 0-5 wt %.

Slag formers may also be provided and are selected from silicon compounds such as elemental silicone; silicon dioxide; silicones such as polydimethylsiloxane; silicates such as potassium silicates; natural minerals such as talc, mica, and clay, and other known slag formers or coolants. The slag former is typically provided at about 0-10 wt %, and more preferably at about 0-5 wt %.

The compositions of the present invention are formed from constituents as provided by known suppliers such as the Nippon Carbide, Aldrich, or Fisher Chemical companies. The compositions may be provided in granulated form and dry-mixed and compacted in a known manner, or otherwise mixed as known in the art. The compositions may be employed in gas generators typically found in airbag devices or occupant protection systems, or in safety belt devices, or in gas generating systems such as a vehicle occupant protection system, all manufactured as known in the art, or as appreciated by one of ordinary skill.

EXAMPLES

The following examples illustrate the benefits of compositions of the present invention:

Example 1

A composition was formed by homogeneously mixing dry copper 5-aminotetrazole at 30 weight percent and dry phase stabilized ammonium nitrate at about 70 weight percent of the total composition. The resultant gas yield was about 88.5% of the total combustion products. The % weight loss when heat aged at 107 C for about 400 hours measured about 0.30 to 0.50 weight percent of the total composition.

Comparative Example 2

A composition was formed by homogeneously mixing diammonium salt of 5,5′-bis-1H-tetrazole (BHT-2NH3) at about 25.8 weight percent, phase stabilized ammonium nitrate at about 65.43 weight percent, strontium nitrate at about 7.47 weight percent, and clay at about 1.3 weight percent, together. The resultant gas yield was about 92% of the total combustion products. The weight percent loss when heat aged at 107 C for about 400 hours measured about 0.20 weight percent of the total composition.

Comparative Example 3

A composition was formed in a similar manner as Example 1 wherein guanidine nitrate at about 53 weight percent and basic copper nitrate at about 47 weight percent were homogeneously mixed together. The resultant gas yield was about 75% of the total combustion products. The % weight loss when heat aged at 107 C for about 400 hours is believed to be about 0.30 to 0.50 weight percent of the total composition.

Example 4

A composition was formed in accordance with the present invention, and in the same manner as given in Example 1. Burn rate tests were performed by employing samples weighing about 2.6 grams, having about 0.45 inches in height, and having about 0.5 inches in diameter. Each respective sample was ignited under the pressures indicated, and the burn rate was thereby measured. The burn rate was about 0.48 inches per second (ips) at 1000 psig; about 0.65 ips at 1500 psig; about 0.72 ips at about 2000 psig; about 0.88 ips at 2500 psig; about 0.82 ips at 3000 psig; about 1.19 at about 4000 psig; about 1.18 at about 4500 psig; and about 1.28 at about 5500 psig.

Comparative Example 5

A composition was formed in the same manner as given in Comparative Example 3. The burn rate was about 0.28 inches per second (ips) at 1000 psig; about 0.30 ips at 1500 psig; about 0.34 ips at about 2000 psig; about 0.36 ips at 2500 psig; about 0.38 ips at 3000 psig; about 0.42 at about 4000 psig; about 0.78 at about 4500 psig; about 0.72 at about 5000 psig; and about 0.46 at about 5500 psig.

Example 6

A composition was formed in accordance with the present invention, and in the same manner as given in Example 1. Differential scanning calorimetry (DSC) evaluations indicated an exotherm at 258.89 C, prior to heat aging as per USCAR requirements. After heat aging at 107 C for about 400 hours, DSC evaluations indicated an exotherm at 266.19 C, thereby exemplifying the thermal stability of the present compositions, before and after heat aging.

Example 7

A composition was formed in accordance with the present invention, and in the same manner as given in Example 1. DSC evaluations indicated an exotherm at about 259 C, but did not reveal a low melting eutectic near or below 107 C. This confirmed that exemplary compositions of the present invention could withstand heat aging at 107 C for 400 hours, as defined by USCAR requirements.

Example 8

A composition was formed by homogeneously mixing dry potassium 5-aminotetrazole at about 23 weight percent and dry phase stabilized ammonium nitrate at about 77 weight percent of the total composition. DSC evaluations indicated a low melting eutectic at about 98.4 C, thereby confirming that this composition would not withstand heat aging at 107 C for 400 hours, as defined by USCAR requirements. No substantial exotherm occurred as in Example 7.

Accordingly, the examples illustrate the enhanced thermal stability of the present compositions. Copper is a desirable element in fuel constituents because of its inherent insulating property and its thermal conductibility. 5-aminotetrazole is also preferred because of its inherent gas generating properties including an abundance of nitrogen for example, and its commercial availability at a relatively inexpensive price. Nevertheless, when copper and 5-aminotetrazole are combined with phase stabilized ammonium nitrate, concerns such as poor thermal stability arise.

In accordance with the present invention, it has been found that complexing transitional metals such as copper with 5-aminotetrazole results in a plurality of benefits including enhanced thermal stability and enhanced cooling of combustion gases. It is believed that the electron withdrawing nature of the copper (or transitional metal center of the complex) draws electron density away from the primary amine group on 5-aminotetrazole. It is thereby believed that this delocalization of electrons on the NH2 group of 5-AT prevents interaction with the acidity of ammonium nitrate, and also enhances the metal ion interaction with the ammonium nitrate.

The examples further exemplify the superior burn rates and ignitability of compositions of the present invention along with the attendant excellent gas generation. Stated another way, improved ignitability of the present compositions is visually observed at ambient conditions, as compared to compositions described in Comparative Examples 2 and 3. It is believed that unlike other compositions containing transitional metal species, the present complexes of 5-aminotetrazole prevent the formation of transitional metal diammines and triammines such as copper diammine. Typically, the propellant will exhibit a blue coloration as the diammines and triammines are formed in solid solution after aging and over time. By complexing the transitional metal salts with 5-aminotetrazole, it is believed that the undesirable formation of the ammines is substantially if not completely inhibited, thereby contributing to increased performance reliability as well. Yet another advantage is the decreased amount of NH3 in the gaseous products, thereby enhancing compliance with USCAR requirements, for example.

It is further believed that a low melting eutectic oftentimes forming at about 100 C with compositions containing 5-aminotetrazole and PSAN is prevented with the present compositions. As a result, thermal stability is enhanced.

As shown in FIG. 1, an exemplary inflator or gas generating system 10, incorporating a dual chamber design, may be manufactured as known in the art. An inflator 12 of the gas generating system 10 will contain a gas generant composition formed in accordance with the present invention. U.S. Pat. Nos. 6,422,601, 6,805,377, 6,659,500, 6,749,219, and 6,752,421 exemplify typical airbag inflator designs and are each incorporated herein by reference in their entirety.

Referring now to FIG. 2, the exemplary inflator or gas generating system 10 described above may also be incorporated into an airbag system 200. Airbag system 200 includes at least one airbag 202 and an inflator 10 containing a gas generant composition 12 in accordance with the present invention, coupled to airbag 202 so as to enable fluid communication with an interior of the airbag. Airbag system 200 may also include (or be in communication with) a crash event sensor 210. Crash event sensor 210 includes a known crash sensor algorithm that signals actuation of airbag system 200 via, for example, activation of airbag inflator 10 in the event of a collision.

Referring again to FIG. 2, airbag system 200 may also be incorporated into a broader, more comprehensive vehicle occupant restraint system 180 including additional elements such as a safety belt assembly 150. FIG. 2 shows a schematic diagram of one exemplary embodiment of such a restraint system. Safety belt assembly 150 includes a safety belt housing 152 and a safety belt 100 extending from housing 152. A safety belt retractor mechanism 154 (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner 156 containing gas generating/auto ignition composition 12 may be coupled to belt retractor mechanism 154 to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners with which the safety belt embodiments of the present invention may be combined are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference.

Safety belt assembly 150 may also include (or be in communication with) a crash event sensor 158 (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner 156 via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner.

It should be appreciated that safety belt assembly 150, airbag system 200, and more broadly, vehicle occupant protection system 180 exemplify but do not limit gas generating systems contemplated in accordance with the present invention.

It should further be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents. 

1. A composition comprising: a first fuel selected from transitional metal complexes of 5-aminotetrazole; and phase stabilized ammonium nitrate as a primary oxidizer, wherein said first fuel is provided at about 5-70% and phase stabilized ammonium nitrate is provided at about 5-70%, said percentages stated by weight of the total composition.
 2. A gas generating system containing the composition of claim
 1. 3. A vehicle occupant protection system containing the composition of claim
 1. 4. The composition of claim 1 further comprising: at least one secondary fuel selected from the group consisting of tetrazoles, metal salts of azoles, nonmetal salts of azoles, nitrate salts of azoles, nitramine derivatives of azoles, metal salts of nitramine derivatives of azoles, guanidines, nitro derivatives of guanidines, azoamides, nitrate salts of azoamides, and mixtures thereof.
 5. The composition of claim 1 further comprising: at least one secondary fuel selected from the group consisting of 5-aminotetrazole, potassium 5-aminotetrazole, diammonium salt of 5,5′-bis-1H-tetrazole, 5-aminotetrazole nitrate, dipotassium 5-aminotetrazole, dicyandiamide, guanidine nitrate, nitroguanidine, azodicarbonamide, azodicarbonamidine dinitrate, and mixtures thereof, said secondary fuel when combined with said transitional metal complex of 5-aminotetrazole provided at about 5-70 weight percent of the total composition.
 6. The composition of claim 1 further comprising: at least one secondary oxidizer selected from the group consisting of metal nitrates, basic metal nitrates, metal nitrites, metal oxides, metal and nonmetal perchlorates, metal and nonmetal chlorates, and mixtures thereof, said secondary oxidizer provided at about 0.1-25 weight percent of the total composition.
 7. The composition of claim 1 further comprising: at least one secondary oxidizer selected from the group consisting of strontium nitrate, potassium nitrate; potassium nitrite; iron oxide; ammonium perchlorate, potassium perchlorate, and mixtures thereof.
 8. The composition of claim 1 wherein said transition metal complex of 5-aminotetrazole is selected from copper 5-aminotetrazole, nickel 5-aminotetrazole, and zinc 5-aminotetrazole.
 9. A composition comprising: copper 5-aminotetrazole complex as a first fuel; and phase stabilized ammonium nitrate as a primary oxidizer, wherein said first fuel is provided at about 5-70% and phase stabilized ammonium nitrate is provided at about 5-70%, said percentages stated by weight of the total composition.
 10. The composition of claim 9 further comprising: at least one secondary fuel selected from the group consisting of tetrazoles, metal salts of azoles, nonmetal salts of azoles, nitrate salts of azoles, nitramine derivatives of azoles, metal salts of nitramine derivatives of azoles, guanidines, nitro derivatives of guanidines, azoamides, nitrate salts of azoamides, and mixtures thereof.
 11. The composition of claim 9 further comprising: at least one secondary fuel selected from the group consisting of 5-aminotetrazole, potassium 5-aminotetrazole, diammonium salt of 5,5′-bis-1H-tetrazole, 5-aminotetrazole nitrate, dipotassium 5-aminotetrazole, dicyandiamide, guanidine nitrate, nitroguanidine, azodicarbonamide, azodicarbonamidine dinitrate, and mixtures thereof, said secondary fuel when combined with said transitional metal complex of 5-aminotetrazole provided at about 5-70 weight percent of the total composition.
 12. The composition of claim 9 further comprising: at least one secondary oxidizer selected from the group consisting of metal nitrates, basic metal nitrates, metal nitrites, metal oxides, metal and nonmetal perchlorates, metal and nonmetal chlorates, and mixtures thereof, said secondary oxidizer provided at about 0.1-25 weight percent of the total composition.
 13. A composition comprising: a first fuel selected from the group consisting of copper 5-aminotetrazole, nickel 5-aminotetrazole, and zinc 5-aminotetrazole; and phase stabilized ammonium nitrate as a primary oxidizer, wherein said first fuel is provided at about 5-70% and phase stabilized ammonium nitrate is provided at about 5-70%, said percentages stated by weight of the total composition.
 14. The composition of claim 13 further comprising: at least one secondary fuel selected from the group consisting of tetrazoles, metal salts of azoles, nonmetal salts of azoles, nitrate salts of azoles, nitramine derivatives of azoles, metal salts of nitramine derivatives of azoles, guanidines, nitro derivatives of guanidines, azoamides, nitrate salts of azoamides, and mixtures thereof.
 15. The composition of claim 13 further comprising: at least one secondary fuel selected from the group consisting of 5-aminotetrazole, potassium 5-aminotetrazole, diammonium salt of 5,5′-bis-1H-tetrazole, 5-aminotetrazole nitrate, dipotassium 5-aminotetrazole, dicyandiamide, guanidine nitrate, nitroguanidine, azodicarbonamide, azodicarbonamidine dinitrate, and mixtures thereof, said secondary fuel when combined with said transitional metal complex of 5-aminotetrazole provided at about 5-70 weight percent of the total composition.
 16. The composition of claim 13 further comprising: at least one secondary oxidizer selected from the group consisting of metal nitrates, basic metal nitrates, metal nitrites, metal oxides, metal and nonmetal perchlorates, metal and nonmetal chlorates, and mixtures thereof, said secondary oxidizer provided at about 0.1-25 weight percent of the total composition. 